This invention relates to multi unit electrical apparatus with forced air cooling.
Multi unit electrical systems are commonly employed to allow the user to tailor a system to his own requirements. A typical application of such a multi unit system is in the field of mass data storage. Typically, a plurality of data storage devices such as magnetic disk drives, are mounted in a box which also incorporates cooling fans and a power supply. The data storage devices may be used together to provide higher reliability by, for example, allowing duplication of information, or else to increase storage capacity. If the storage devices are removable this has the added advantage of allowing the user to remove and replace defective devices, or to lock away devices containing especially sensitive information. However, enclosing one or more devices and power supply within a single box imposes restrictions on the ability to maintain the devices and power supply within safe operating temperatures. Thus forced air cooling will usually be necessary.
An example of such a data storage system is described in European Patent Application number 320 107 in which five 5.25 inch disk drives are removably mounted in the front of a drawer, the rear of which contains a power supply. Cooling of the power supply and devices is provided by two axial fans fixed into the rear bulkhead of the drawer which pull air past the devices and over the power supply.
A second example is described in European Patent Application number 328 260, in which two customer removable data storage units in canisters are mounted in the front of a drawer. A power supply is located at the rear of the drawer separated from the devices by an internal bulkhead in which are located two axial fans for providing forced air cooling. While different device types may be mounted inside a common canister, no provision for devices having different cooling requirements is described in the application.
The reliability of a cooling system is important. European Patent Application number 320 720 describes a computer cooling system using two centrifugal fans, both of which normally operate at reduced capacity. A control system automatically detects the failure of one fan and increases the speed of the other, to maintain a substantially constant flow of cooling air through the computer.
Removal of one or more devices would also cause an imbalance in the air flow. IBM Technical Disclosure Bulletin ("Gate/Shutter Airflow Control Device", August 1989 pp 346-347) describes the use of a shutter which blocks off holes in a bulkhead when there is no device in that position.